503
Thz Canadian M inerala g i st vol. 34,pp. 503-512 (1996)
COBALTITE-GERSDORFFITESOLID SOLUTION AS A PRIMARYMAGMATIC PHASE IN SPESSARTITE, LACAUNEAREA, MONTAGNE NOIRE, FRANCE
DIDIER BENAT, PIERREMONCHOIIX ANDFRANCIS TOLLON
Leboratoire de Minzralogie et Cristallographie, UMR 5563, UniversitC Paul Sabatier, 39, AIIdes Jules Guzsde, 31000 Toulouse Cedex, France
AssrRAc"r
A cobaltite-gersdorffitesolid solution occursin spessartitesills from the l,acaunearea, Montague Noire, southemFrance, enclosedwithin phenocrystsand found in the matrix. It commonly enclosesrounded grains of pyrrhotite with lamellae of pentlandite.Compositional variation of cobaltite-gersdorffiteois representedmafuly by a Co-for-(Ni + Fe) substitution;the core is cobaltjferous,and the rim, nickeliferous.Atomic proportionsin the structuralformula as obtainedfrom over 80 analyses, vary witlin the following ranges:(Co6.s5-o5y'.{ie.27-a.66Fes.1o-a.3)As6.e7-1.67S0.se-o.sz. The Ni/Fe value is near 2, which could indicatethe presenceof a (1.{io.*Feo.u,)Aiscomponent witl a Ni-Fe order in the Ni site. Textural evidenceand compositional data suppofi an igneous rather rhaa secondaryorigin. Cobaltite-gersdorffite* can crystallize by separationof an early immiscible sulfaxsenideliquid from a calc-alkalinelamprophyric magma. These sills could representan atffactivetarget for Au prospectingin the MontagneNoire area.
Kewords: cobaltite,gendorffite, solid solution,pdmaxy, spessartite, Montagne Noire, France.
SoMlr,tans
Une solution solide de cobaltite-gersdorftitese rencontredans un sill de spessartitede la r6gion de Lacaune,Montagne Noire, partie sud de la France, soit inclus dans les phdnocrisaux, soit dans h pate. Ce mindral renferme fr6quemmenten inclusion des grains arrondis de pyrrhotite avec des lamelles de pentlandite.Sa variation en composition est repr6sent6e essentiellementpar une substitution Ce-(I.{i + Fe), avec un coeur cobaltif?re et une bordure nick6lifbre. l,es formules structurales, obtenues i partir de 80 r6sultats d'analyses, varient dans les intervalles suivants: (Coo.os+.ssl.{h.zz+.66Fee.1an3)Ass.gr_r.o:So.:g_o.s7. I,e rapport NilFe est toujours voisin de 2, ce qui pourrait indiquer I'existence d'un Comfosint (Nh.orFq.::)AsS avec mise en ordre de Ni et Fe sur le site Ni. l€ur compositionet leur relation avec les ninerauiprimaires riigmatiques indiquent qu'ils sont le r6sultal d'un processusign6 plut6t qu'hydrothermal.Les solutions solidescobaltite-gersdorfftte cristalliseraient i partir d un liquide sulfo-ars6ni6,s6par6 pr6cocement par immiscibilit6 du magma lamprophyriquecalco-alcalin. Ces sills de spessartitepeuvent repr6senter une cible intdressantepour la prospectionde I'or en MontagneNoire.
Mots-cl6s:cobaltite, gersdorffite, solution solide,primaire, spessartite,Montagne Noire, France.
Ir.rrRooucilolI unusualoccurence will be usedto discusstheir origin: is the cobaltite-gersdorffrte,, a primary magnatic The occurrence of cobaltite-gersdorffite solid- phaseor a hydrothermalphase? solution in basic and ultrabasic rocks is generally consideredto be of hydrotherrnal oigtrn (Oen et al. Ttn Hosr SpsssARTrE 1971,Penuk et al. 1971,Oen 1973,Besson & Picot 1975, Leblanc 1986, Gervilla 7990, kfchard et al. The cobaltite-gersdorffrte* occurs in spessartite 1994). Occasionally,lamprophyric rocks may contain emplacedin Lower Cambriancarbonate formations in primary magmatic sulfides, generally pyrrhotite, the Lacaune area, Montagne Noire, southemFrance. pentlandite and chalcopyrite (Grosser 1966, Rohde B6aat et al. (1993) have described the geology, lglZybut magmaticco6altite-gersdorffite* has never mineralogy and geochemistryof the host spessartite, beenreported. and proposedthatit couldhave beenderivedby partial In this paper,we report new information (composi- melting of a metasomatically enriched garnet + tional variatiols s1d 26ning) on sulfarsenideminerals pblogopite t amphibole lherzolite. The water-rich found in sills of spessartitefrom the Lacaune area, nature of the magma is clearly indicated by the Montagne Noire, in soutlern France. Features of presence of hydrous mafic phenocrysts and by 5M TIIE CANADIAN MINERALOGIST plagioclase occurring only in the groundmass(c/. mica, quartz and apatite. Ocelli of light brown mica, Burnham1979, Nlan & Carmichael1984). commonly including microcrystals of cobaltite- Spessartitebelongs to the calc-alkalinesuite. It gersdorfflte., in their core, also are found. These containsamphibole (magfresio-hastingsite to pargasite) ocelli are interpretedas the product of transformation and phlogopite as phenocrysts, both commonly of relict olivine phenocrystsduring the ascentof the including microphenocrystsof chromianrutile, zrncian magma. chromite and cobaltite-gendorffite"., with occasional A very subordinate,secondary assemblage,with inclusionsof pyrrhotite. However,sulfarsenide-sulfide colorless amphibole, talc, chlorite, white mica, grains and oxide grains occur in separateinclusions. carbonateand pyrite, is found only near the veinlets The groundmasscomprises plagioclase, light brown within the fresh rock.
Fto. 1A. Photomicrographsof grain of Ni - Co - Fe sulfarsenide.Secondary electron image of a subhedral grain of cobaltite-gersdorffiteoand correspondingNiKo, CoKo and FeKcrmaps showing an oscillatory zonation. PRIMARY COBALTITE-{ERSDORFFITE. MONTAGNE NOIRE s05
Conar-rnr-GnnsDoRFFTTEss and Co, CuFeS2for Cu, Fe and S, FeAsSfor As, and Sb2S3for Sb. The data were corrected using PAP Mineralogy and textures (SX50) procedures.Concentrations of major elements are accurateto x.1wtvo of the elementpresent, whereas The average spessartitecontains less than 0.17o concentrationsof minor elementsate less accurate,but by volume of cobaltite-gersdorffite"r.It occurs as arereproducibleto *0.1 wt%o. inclusions50 to 250 pm acrosswithin amphiboleand, Representative compositions of cobaltite- more rarely, within phlogopite phenocrysts,in the gersdorffrte.,and sulfides are given in Table 1. The ocelli of light brown micA and also in the matrix. cobaltite-gersdorffite., is a solid-solution series The grains of cobaltite-gersdorffite* appear white, between (Ni,Fe)-rich cobaltite and gersdorffite. with high reflectance and weak anisotropism.They Compositional ranges of Co, Ni, Fe, As and S, as occur as euhedral to subhedral single crystals obtained from 80 analyses (Fig. 2), are @gs. 1A, D) or in small aggregatesand, more rarely, (Cos.e5-a.5el'{is.n 4.66F eo.v+.3)Ase.y-r.s7Se.se-o.rr. as subsphericalgrains (Fig.lB). No evidence of Sb contentsinvariably arelow (maximum0.5 wtVo). exsolutionis visible, even at 500x magnificationwith Sb enters the cobaltite-gersdorffiless structure by the scanning electron microscope,in secondary- substitutionfor S (Fig. 3). As shown in Figure 4, the electron images (Figs. 1A, C). The crystals of degree of substitution of As for S increaseswith cobaltite-gersdorffrte*occasionally contain amphibole increasing(Ni + Fe) contents,in agreementwith the and phlogopite crystals as inclusions, as well as experimentalresults of Maurel & Picot (1974). rounded grains of pyrrhotite with lamellae of Dependingupon the silicate assemblagein which pentlandite(Frg. 1C). they occlu (phenocryst$, ocelli, groundmass), cobaltite-gersdorffite., shows distinct compositions Mineral chemistry (Frg. 2). The grains in the groundmassare Sb-poorto Sb-bearinggersdorffite (0.13-{.50 fi7o), with a As/S More than eighty elecuon-microprobe analyses value greaterthan 1.06.They are poorly zoned,with a were doneusing a CAMEBAX SX50 at the Laboratory core slightly more Co-rich than the rim (anal. 5 and 6, of Mineralogy, Toulouse (beam current of 20 nA, Table 1). The grains trappedin the phenocrystsor in 25 kY, with a counting time of 10 s at the peak the ocelli of light brown mica generally exhibit a positions and 5 s for symmetricalbackgrounds). The normal and discontinuouszonation between a large following standardswere used: pure elementsfor Ni core of Sb-poor, (Ni,Fe)-rich cobaltite with an As/S value less than 1.06 and a narow rim of gersdorffite (Frg. lD, anal. I to 3 in Table 1). More rarely, they exhibit, in addition, a nturow externalrim that is more cobaltiferous than gersdorffite, or even oscillatory zonation (Frg.lA). The maximum variation (e.g., anal. la to ld in Table 1) is as wide as the intergrain variation. The solvi in the systemNiAsS - CoAsS - FeAsS have been experimentally determined by Klemm (1965). There is complete miscibility between gersdorffite and cobaltite above 550oC. On the contrary, miscibility between arsenopyrite and cobaltite and betweenarsenopyrite and gersdorffiteis limited, particularly at low temperatures,because of differences in the crystal structureso pseudo- orthorhombic for arsenopyrite, pseudocubic for cobaltite and gersdorffite (Permingeat1991). As
Ftc. 18. Photomicrograph of subspherical grain of cobaltite-gersdorffite*. 506 TTIE CANADIAN MINERALOGIST
FIc. lC. Photomicrographsof grain of Ni - Co - Fe sulfarsenide.Secondary electron image of cobaltite- gersdorffite* crystal including phlogopite(Ph) and pyrrhotite(Po) with lamellaeof pentlandite(Pn), and correspondingNiKo, CoKoand FeKcl maps. shown in Figure 2, our compositions of cobaltite- different types of As-S ordering @ayliss 1982b).For gersdorffitessplot, with few exceptions,in a region that cobaltite,only thePca2l stucture ha$been determined would be in a single-phasefield at 500'C, and thus (Bayliss 1982a). Bayliss invoked a chemical reason suggestthat crystallization occurredat high tempera- to explain the order of As and S: "Since Fe (acid) may tures(500'C). be classifiedas harder than Ni, andS (base)is probably The average Ni/Fe value near 2 @ig. 2) could harderthan As, it is possiblethat Ni may occur in an indicate a solid-solution series between CoAsS and As-rich environmentand Fe in a S-rich environment". (Nio.uuFeo.rr)Ass.For gersdorffite, three crystal Nevertheless,according to the crystallographicdata sffuctures correspondingto tle space groups P213, obtained for these specimens,he comes to the Pca2t and, Pa3 have been described, based upon conclusion tlat Ni and Fe are randomly distributed PRIMARY COBALTITE-CERSDORIIFTTE,MONTAGNE NOIRE 5W
Ftc. lD. Photomicrographsof grain of Ni - Co - Fe sulfa$enide. NiKo and CoKcr maps of a euhedralgrain of cobaltite- gersdorfflte* showinga normal, discontinuouszonation. Scale bar: 100 pm. amongthe four metal sites.However, the samplesused Vinagradova and Kroutov (quoted in Kostov & by Bayliss come from different localities and show Minceva-Stefanova1981), and those from the Mdlaga different values of the Ni/Fe ratio. On the other hand, province,Spain (Oen et al. L97L,1973,Gervilla 1990, our cobaltite-gersdorffrtessdata, just as the data of Gervilla & Rgnsbo L992) and the Cobalt-Gowganda Vinagradova and Kroutov (quoted in Kostov & district, Ontario @effiik et al. 1971).On the otherhand, Minceva-Stefanova1981) and those of GenilTa et al. the cobaltite-gersdorffite.. from Lacaune clearly (1996), plot very close to the Ni/Fe = 2 line; the differs from that in Morocco @ermingeat1991) by its (1.[iq.66Fee$)Asscomponent can be interpretedto have higher Fe contents(Ftg. 2). a PcaZr structure,with Ni-Fe order at the Ni site. Becausethe fine grain-sizeof pyrrhotite, contami- In comparison with available compositions of nation by the host cobaltite-gersdorffite..is possible. cobaltite-gersdorffite* taken from the literature, our However,analyses of relatively largegrains (40 pm) of cobaltite-gersdorffite,"data mostly ovedap those of pynhotite indicate the systematicpresence of Ni and
TABLE I. RSPRBSB\TTAITqB RBSULTS OF ELBCTRON-MCROPROBE ANALYSES, CoBALTITB-CERSDORFFNEdB AND ASSOCTATEDST'LFIDES FROMTITE LAC.AUNEAREA MONTAGMNOIRE
Alal la lb lc ld 2t b 34 3b M 4b 5a 5b @ 6b I I 9 10 Phe Cdc Co/c Cet Cet Oo/c Ceh Co/c Geh Gelo Gg/r Ge/c Ceh Gelc Ge./r Po/c Po/c Po& Pdc IIost O O O o O o m Ph AnahAmph M M M M Gs CGs S"' Po
Nt 9.83 tt.tt 2132 ?2Es 10.83 r4.@ 1030 17.01 15.86 m.67 19.@ 21.01 23.15 n'.8 Llo 0.61 1.11 30.E2 Co 2t.39 t8.U 3.10 236 t952 r4.& 10.49 98 ,253 3.n 629 4.t3 L.q 2-12 0.O7 nd D.d 0.46 Fe 4.96 5.47 10J9 9.97 5.97 6.98 5.?5 9Zl 7.72 10.86 9.A 10,93 10.14 9.Sl 5730 58J5 5836 34.00 sb a2t 0.13 vrs 0.41 0.14 0.t2 0.0E 0.r0 0.u 0.19 02tt 0.13 0.32 0.37 0.m 0.@ 0.m 0.m As 45.35 45s2 68 46,g2 4513 45:n 45J0 46.f/ 45:75 47.14 45.75 6,6 &92 47.% L72 l.m 058 r33 s 19.Ot 19.06 1833 17.93 t&76 1850 1899 19.01 1EJ5 1E30 1822 n& 17.32 nAs 38,94 39.n 39fi ne
Total 100.781m.E9 [email protected] 1m34 1(n95 100,33 101.11100.74 1@J6 t@53 9.43 99s8 WtI 100.421m53 99.48 935 tmc6
Atons per fcnmla unif
Ni 027 033 0.60 0.64 0J0 0.40 o8 oA7 0.44 058 053 0J9 0.65 0.& 0.0r 0.01 0.()2 Lt3 Co 0J9 051 0.@ 0.6 0J3 0.40 0J6 O2S 034 o.O9 0.18 0.11 0.05 0.06 0'00 0'03 Fe 0.14 0.16 0,31 029 0.17 0r0 0.16 on 022 0:,2 oD 0.30 0.30 030 043 0,85 0.85 L47 As 0.98 o.9S 1.03 1.03 0.98 0,9 0.n 1.00 0.98 l.gt 1.m LV2 1.03 1.6 0.o3 001 0.01 0.0r/ s 0.96 0.96 o.g4 0.92 0.94 0.93 0.95 o.n 0.93 0.95 0.94 0.91 0.89 0.92 0.97 0.9 099 429
Stuc0ralformtr,e4roesedinabnspcfclrqlamit,rrcooaloilmrl@fubasbd(l)Ni+Co+Fe-Iafon(P€minged191)fEsolldsolltioB(@J betye€ncobslie(Co)odgersdfitrte(Ge),(2)S+As-lalomtorpydsdr6,d(3)ebtalofgdoosfs@[email protected]:co€(c)andrin(r)of propordm of c$alfte-gersddbs cystal hftded in Flogqits G0 d an@ots (Anph) lhtnsysts, @tli (O) dd mdh (MI nd.: not d€tedEd. ft o@ltihfib is qoiled in welgt[ %. 508 TIIE CANADIAN MINERALOGIST
fGtS
FeAsS
Nl/Fe = 2
":j CoAcS wol% NIAsS Ftc. 2. Compositionalplot of cobaltite-gersdorffite*in the CoAsS- FeAsS- NiAsS system.Sohus lines at 400o,500o, 600o and 650'C (inset) are taken from Klemm (1965). l,egend: core (O) and rim (O) of cobaltite-gersdorffite* included in amphibole or phlogopite phenocrysts;core (A) and rim (A) of cobaltite-gersdorffits$included in ocelli in mica; (D cobaltite-gersdorffite* included in the groundmass.Fields Ia and Ib: cobaltite-gersdorffite* from Morocco @ermingeat l99l), tra and IIb: cobaltite-gersdorffiteofrom Cobalt-Gowganda(Pefuk a al. l97l), Itr: cobaltite-gersdorffite* from Mllaga (Oener a/. 1971,l973,Gewtl1a 1990,cervilla & R6nsbo1992), IV: stippledfield, dataof Vinagradovaand Kroutov (in Kostov& Minceva-Stefanoval98l).
As (0.5 to l.l wt%oNi, 0.5 to 2.7 wt%oAs, Table 1) magmaticFe-Ni-sulfides that havebeen modified by a and the absenceof Co. Very fine-grainedpentlandite As-Co-rich fluid penetratingalong the cleavageplanes (5 pm) shows a fairly constant composition, with a of the phenocrysts,and probably responsiblefor the Ni/Fe valuenear 0.9 (Tablel). very subordinate secondary assemblagepresent in - the spessartite.Pynhotite and pentlandite enclosed DlscussloN in cobaltite-gersdorffite,. would be relics of this magmatic stage. We can also suggest a reaction The occurrenceof cobaltite-gersdorffiter"in basic between a high-temperatureore fluid and the water- and ultrabasic rocks is generally attributed to a rich lamprophyricmagrna. However, such a hypothesis hydrothermalprocess except for instance,in therzolite does not explain both intragrain and intergnin from the Milaga provinceowhere Gervilla & Rpnsbo variations, Le., neither the systematicallyhighest Co (1992) relatedthe Fe-rich cobaltite-gersdorffiteoto a content of the core of the grains nor its systematic late-magnnaticprocess, with a temperatureof crystal- partition betweencobaltite, for the grainstrapped in the lization as high as 700'C. phenocrystsand the ocelli, and gersdorffrtefor those According to the hydrothermal hypothesis, hostedin the matrix. In addition, in the hydrothermal cobaltite-gersdorffiter" could represent original hypothesis, one would expect that additional PRIMARY COBALTITE-{ERSDORFFITE" MONTAGNE NOIRE 509 s e 0.4 rr c, 10 o'ooA E03 trtr A tr O A q Ftc. 3. Plot with regression coefficient describing oo the relationshipbetween weight percent Sb and S in cobaltite- gersdorffiterr. We use wtTo instead of atomic proportions because of fte low contentsof Sb.
chalcophileand siderophileelements would be carried panidiomorphic texture, (3) the large and regular by the fluid phase@leet L977,I*blanc 1986,Stone compositionalvariation (Ftg. 2) betweenthe cobaltite et al.1989). hostedin the phenocrystsand the gersdorffttehosted in A magmaticorigin for the cobaltite-gersdorffite..of the matix, reflecting a temperatue decreaserelated to *late" Lacaunecould theoreticallyaccount for the following a magmatic fiend, from "early'' Co-rich to features: (1) the presenceof cobaltite-gersdorfftte* Ni-rich crystals, (4) the crystallochemicalfeafures of grains enclosedby primary magmatic amphiboleand the associatedzincian chromite (with up to 4.5 wt%o phlogopitephenocrysts, associated with high-T phases ZnO); Naldrett (1979) has shownthat in hydrothermal like pyrrhotite,pentlandite, chromite and Cr-rich rutile, ores,7,n is preferentially partitioned with Cu and Fe (2) its occunencein an undeformedrock showing a into sulfide phases,whereas in orthomagmaticores,
a E i.1o
t) tr
I 6T a O
Fro. 4, Relationship 1.00 betweenAVS and (Ni + 0.60 0.80 Fe) in cobaltite-gers- Ni + fe (atomsper formula unit) dorffite*. 510 TTIE CANADIAN MINERALOGIST
it is preferentially partitioned into chromian spinel. arsenic-richmantle-derived magmas have never been Zn-ich chromite associatedwith Fe-Ni sulfides and reportedowe suggestthat arsenicand sulfur could have Ni-Co arsenides in ultrabasic rocks have been been introduced during metasomatismof the mantle describedin several ore deposits (Klemm & Weiser sourceby fluids derivedfrom a subductedslab. 1965,Groves et al. 1977.Oen & Kieft L977.Leblanc Rock et al. (1989) have discussedthe commonlink 1986, Gervilla 1990).Johan (1980) has proposeda betweengold minsp[2ation andlamprophyres. Tollon crystallochemicalmodel for spinelthat allows us to dis- (1969) and B6 at & Monchoux(1991) also pointed criminatebetween that occurringin Ni{u-mineralized out the presenceof metabasicrocks with chromian complexesand that in barrenmafic intrusions,based on and zincian spinel in the gold-bearing As-S their mg-numberand Al{r contents.According to this mineralizationof the Salsignedistrict. As the result of model, the cbromite of Lacaunewould correspondto geochemical prospecting carried out in Montagne spinel in mineralizedcomplexes @€zi* et al. 1993). Noire (Michard 1990), two zones with As and Au Moreover, experimental studies on gersdorffite anomalieswere discovered,one obviously centeredon (Yund 1962)and cobaltite(Ilaurel & Picot L974)have the Salsigne district, the other on the Lacaune area. shown that thesephases can be stableat temperatures Hence, the spessartitesills from the latter areaowith as high as 700oand 1000'C,respectively, and 850'C higher contents of gold and arsenic (2.9-5 ppb and for the Pca21 crystal-structure(Kostov & Minceva- 30H50 ppm, respectively)than cornmonbasic rocks, Stefanova1981). and the associated surficial As-Au anomalies" Gervilla et al. (1992)observed separate associations constitute a potential exploration guide for Au-As-S of arsenidesand sulfides in the ore depositassociated mineralization. with ultramafic rocks of Beni Bousera,in Morocco. They suggestedthat this could be the result of Coucrusroxs immiscibility and gravity separation of t}le denser As-liquid from the S-dominant liquid, inducing the Resultsof our study indicate that the occurrenceof early crystallizationof arsenides.Contrary to the Beni cobaltite-gendorffiter. in basic rocks like spessartite Bousera ultramafic rocks, the cobaltite-gersdorfftte* can result from orthomagmaticsegregation, through in the Lacaunelamprophyre suggests a crystallization formation of an early immiscible sulfo-arsenideliquid from a single liquid. Acceptingthe model of magmatic from a nearly primitive, calc-alkaline lamprophyric segregation,these different textural relationshipscould magma, as well as by secondary @ydrothermal) be explainedby a differenttiming 6f crystallization: processes.Textural relationships and compositional after the unmixing of the As-S liquid in the Beni features of cobaltite-gersdorffiter, $uggest that the Bousera ore, before at Lacaune. According to the cobaltite crystallized early as high-temperaturesolid- water-rich characterof the silicate magma(cf Naldrett solution crystals, and then the gendoffite formed 1969), the cobaltite crystallized early from the As-S contemporaneouslywith the matrix, and quenched liquid, and waspresent at the onsetof crystallizationof upon cooling. Such an early crystallization of the hydrousmafic phenocrysts.Before the trappingby cobaltite-gersdorffite,,could be due to the water-rich the phenocrysts, the Ni-rich residual As-S liquid characterof the magma. would have been partially removed during the magma's ascent and would have crystallized later, ACKNOWLEDGEMENTS contemporaneouslywith the matrix, thus forming the gersdorffrte.Such a hypothesissupports the observed The authorsare gratefirl to M. Benvenuti,J. Guha discontinuouszonations, these being preservedby the and D.C. Harris for critical commentsand corrections. rapidcooling. We also thank the referees,Y. Mo61o,Z. Iohan alid Various geneticmodels have beenproposed for the R.F. Martin, for the numerouscomments that greatly origin of sulfur and arsenic in magmas (Oen 1973, improvedthe manuscript. Haughton et al. 1974, Rajamani & Naldrett 1978, Naldrett 1981,Stone et al. 1989.Gervilla & Leblanc 1990,Leblanc et al. 1990).For instance,Duke (1990) REFERENCES proposedthat crustal sulfur was assimilatedat depth, prior to fractional crystallization,whereas Gamti et al. AnAN, J.F. & CARrrflcHAEL,I.S.E. (1984): l,amprophyric (1984)prefened a mantleorigin, as did Lorand(1987) lavas in the Col'ima graben, SW Mexico. Contrib. and Gervilla & Leblanc (1990).The mineralogicaland Mineral. Petrol. 8, 203-21,6. chemical features of the Lacaune lamprophyre are consistent with a primary magma derived from a BAyLIss,P. (1,982a):A firther crystal structurerefinement of metasomaticallyenriched phlogopite + garnet I cobaltite.Azn Mineral. 67. lM8-1057 . amphiboletherzolite @6ziat et al. 1993). Since low- field-strengthelements can concentratein thesetypes (1982b): A further crystal structurerefinement of of magma (e.9., Perfit et al. L980), and although gersdorffite.Are. Mineral. 67, 1,058-10il. PRIMARY COBALTITE-{ERSDORFFITE" MONTAGNE NOIRE 511
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